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Thursday, 11 August 2011

When choosing a gas or wood-fired stove its capacity is a determining factor. Many people are unaware that an average living room space only requires 3 to 4 kilowatts (kW) to heat it. This is especially true in today's well-insulated homes and, given the fact that many homes already have central heating; the fire is often just used for additional heating.

Yet consumers often go for a too high a capacity, with the risk that they subsequently use the fire sparingly or can only burn at a low degree, otherwise it would become too hot for the room. With wood-fired stoves and heaters this results in poor combustion, blackened glass and high emissions. With gas fires, it particularly means you don't get to enjoy the lovely flame effect these fires have to offer.

Calculating the capacity needed to heat the space you have in mind is very easy. The graph shows the capacities indicated in kWs. The space to be heated is indicated in cubic metres (m3). The number of cubic metres is determined by multiplying the length, width and height of the space. You can then read the capacity you require at the intersection of one of the three lines. Which of these three lines you select depends on the degree to which your home is insulated.

Your home is:

A

Well insulated

Is double-glazed

Has floor and wall insulation

B

Is reasonably insulated

Has minimal double glazing

Has minimal floor and wall insulation

C

Poorly insulated

Has no double glazing

Has no floor and wall insulation

The image on the right shows the three situations, A being the red line, a well insulated, double glazed property, B is a reasonably well insulated property in orange and C is a poorly insulated property, perhaps similar to an older property in yellow.

As you can see that depending on room size the heat output required varies considerably, with the average 30m3 living space in a well insulated home only needing around 3kW.

Open and closed combustion

In addition to this, the choice between open or closed combustion is equally important. 'Open combustion' may lead you to think we are talking about an open fire, without a glass front, but this isn't the case. Open combustion is the name given to the system whereby air is extracted from the room in which the fire or heater is positioned, and where the flue gases are removed via a single flue.

What types of stoves are there?

Wood fires and stoves always have an open combustion system. It is important to know when choosing your wood fire or stove that good ventilation in the home is a prerequisite. When a home is well-ventilated you can always install a wood fire or stove. In exceptional circumstances, such as homes with a so-called 'Balance Ventilation System' there are fires and stoves with exterior air feeds. An increasing number of fires and stoves are equipped with such an exterior air feed, or offer this as extra. With this system the combustion air is extracted from outdoors. Please take into account that with a wood firer or, the flue must always go upwards, through the roof and outdoors, and must even reach above roof ridge height.

On the other hand with gas fires and stoves, there is the choice of closed combustion, whereby the requisite combustion air is directly extracted from outside and the flue gases are removed via the same flue. Such extraction can, in many cases, be simply fed through the outside wall or roof. This means you have more flexibility in the exact positioning of your fire. As the system extracts oxygen from outdoors and not from the room where the stove is placed, the system is also ideally suited to the modern, well-insulated and mechanically ventilated home. In the case of gas fires and, you will always be advised to opt for closed combustion. However, if you wish to connect a gas fire or stove to an existing chimney with a diameter of less than 150 mm, then open combustion may well be an option as this requires a smaller flue.

We hope this gives you at least a rough idea of what sort of fire you want and need. The next thing to do is to go online and have a look at what appliances are out there that suit your needs.